Initial Branch Research Articles

Flow-induced vibration of a trapezoidal cylinder at low Reynolds numbers

This paper discusses the flow-induced vibration of a freely vibrating trapezoidal cylinder with a mass ratio of 10 at low Reynolds numbers (Re = 60–250). Over this range of the Reynolds number, we discuss the inflow and transverse amplitudes, frequency ratios, hydrodynamic forces, phase differences, and vortex modes. Comparing to square/circular cylinders with the same flow conditions, responses of the trapezoidal cylinder are much different. In both the vortex-induced vibration (VIV) and galloping regimes, double rise-up of the amplitudes and hydrodynamics forces is observed with respect to Re, as well as the two lock-ins for the frequency ratios. The phase differences and vortex modes in the wake are also found to be different from the square/circular cylinders. Thus, seven flow branches are identified, i.e., the initial branch, upper branch, lower branch, desynchronization region, initial galloping, upper galloping, and high galloping. Then, in order to interpret these branches, the evolutions of vortex formation and shedding in the wake are analyzed. It appears that the asymmetry of the trapezoidal cylinder to the inflow is the direct cause. In addition, a small degree of hysteresis is observed in the VIV regime and a larger degree is observed in the galloping regime.

Flow-induced vibrations of a pair of in-line square cylinders

Flow-induced bidirectional vibrations of two in-line square cylinders of same size and mass ratio (=10) are analyzed at Reynolds number, Re = 100. The cylinders are located in the co-shedding regime, i.e., they are separated by a normalized center-to-center spacing of 5. The reduced speed, U*, is varied from 3 to 15 keeping Re constant. The upstream and downstream cylinders display identical frequency characteristics with U*. Accordingly, the cylinders share identical decomposition of dynamic response. The response is composed of the desynchronization regimes and lower branch; an initial branch does not exist. The vibrations are hysteretic at the lock-in boundaries whereas for a single square oscillator, hysteresis is identified only near the onset of lock-in. Hysteresis in the solutions for U*=7 within the lower branch is reflected in the wake mode of the rear cylinder whereas for the upstream cylinder, wake mode remains identical. The vortex-induced vibration (VIV) of the upstream cylinder is qualitatively similar to that of an isolated square oscillator. Despite the range of lock-in of the cylinders being identical, the VIV of the downstream cylinder departs significantly from its upstream counterpart. The shear layers separated from the front cylinder impinge on the rear cylinder and alter its flow field. The rear cylinder executes high amplitude VIV over the entire lower branch. The symmetry of the drag-lift phase diagrams does not necessarily translate to symmetric phase plots of in-line and cross-stream response. The drag and in-line response of the cylinders are out of phase throughout.

Cyclic behaviour and hysteretic model of austenitic stainless steel bolted T-stubs

The aim of this paper is to investigate the hysteretic behaviour of stainless steel bolted T-stub connections. A total of 22 bolted T-stubs in austenitic grade EN 1.4301 were tested under monotonic loading and cyclic loading under both variable and constant amplitudes. The tested T-stubs were carefully designed with two different bolt configurations and were fabricated with two types of stainless steel bolts – A4–70 and A4–80 thus allowing different failure modes to be obtained. Three additional bolted T-stubs in carbon steel grade Q345B were used as benchmark specimens to facilitate a direct comparison of the performance of carbon and stainless steel T-stubs under cyclic loads. Monotonic loading tests were conducted to acquire basic parameters of the cyclic loading protocols employed in the cyclic loading tests. The hysteretic responses of the tested T-stubs under two variable amplitude loading histories and three proportional constant amplitude loading histories were recorded and were further analysed in terms of failure characteristic, hysteresis response, skeleton curve, energy dissipation and strength degradation. Based on the evolution of the hysteresis curves, standard hysteresis loops were acquired and were used to develop a novel hysteretic model able to simulate the initial loading branch, the unloading branch and reloading branch of the hysteretic response. It has been demonstrated that the developed hysteretic models provide a close agreement with the obtained experimental results and can thus be used to estimate the expected energy dissipation of bolted stainless steel connections subjected to cyclic loads.

Long-term fate of aortic branches in patients with aortic dissection

ObjectiveLate morbidity and mortality related to aortic branches in patients with aortic dissection (AD) have not been well described. We investigated the fate of aortic branches in a population cohort of patients with newly diagnosed AD. MethodsWe used the Rochester Epidemiology Project record linkage system to identify all Olmsted County, Minnesota, residents with a diagnosis of AD from 1995 to 2015. Only patients with >30 days of available follow-up imaging studies were included in the present analysis. The primary outcome was freedom from any branch-related event (any intervention, aneurysm, malperfusion, rupture, or death occurring after the acute phase >14 days). The secondary outcome was the diameter change in the aortic branches. Univariate and multivariable Cox proportional hazards models were used to identify the predictors of branch-related events. Univariate and multivariate linear regression models were used to assess the aortic branch growth rate. ResultsOf 77 total incident AD cases, 58 patients who had survived and had imaging follow-up studies available were included, 28 (48%) with type A and 30 (52%) with type B AD. The presentation was acute in 39 patients (67%), 6 (10%) of whom had had branch malperfusion. Of 177 aortic branches involved by the AD, 81 (46%) had arisen from the true lumen, 33 (19%) from the false lumen, and 63 (36%) from both. After the acute phase, freedom from any branch-related event at 15 years was 48% (95% confidence interval [CI], 32%-70%). A total of 31 branch-related events had occurred in 19 patients within 15 years, including 12 interventions (76% freedom; 95% CI, 63%-92%), 10 aneurysms (67% freedom; 95% CI, 50%-90%), 8 cases of malperfusion (76% freedom; 95% CI, 61%-94%), and 1 rupture (94% freedom; 95% CI, 84%-100%). No branch-related deaths had occurred. Type B AD (hazard ratio [HR], 3.5; 95% CI, 1.1-10.8; P = .033), patency of the aortic false lumen (HR, 6.8; 95% CI, 1.1-42.2; P = .038), and malperfusion syndrome at presentation (HR, 6.0; 95% CI, 1.3-28.6; P = .023) were predictors of late aortic branch-related events. The overall growth rate of aortic branches was 1.3 ± 3.0 mm annually. Patency of the aortic false lumen, initial branch diameter, and Marfan syndrome were significantly associated with diameter increase. ConclusionsIn patients with AD, aortic branch involvement was responsible for significant long-term morbidity, without any related mortality. Type B AD, patency of the aortic false lumen, and malperfusion syndrome at presentation resulted in a greater risk of branch events during the long-term follow-up. Dilatation of the aortic branches was observed in one third of cases during follow-up, especially in the case of a patent aortic false lumen or the presence of Marfan syndrome.

Experimental and computational investigation of interactive flow induced oscillations of two tandem rough cylinders at 3×104≤Re≤1.2×105

The interactive flow induced oscillations (FIO) of two adjacent, elastically mounted, rigid, tandem, locally-rough cylinders in transverse flow direction are analyzed utilizing two-dimensional Unsteady Reynolds-Averaged Navier-Stokes (2-D URANS) equations and verified experimentally in the proximity-wake region. Three sets of experiments and simulations (K = 600N/m, ζ = 0.14; K = 600N/m, ζ = 0.26; K = 1,200N/m, ζ = 0.26; K is spring stiffness, ζ is damping ratio) of two tandem cylinders with turbulence stimulation are tested and simulated for Reynolds number in the range of 30,000 = Re ≤ 120,000. The reduced velocity range is U* = 2.48–14.22, the mass ratio is m* = 1.343, and the center-to-center in-flow spacing to diameter ratio is d/D = 2.57. The characteristics of amplitude response, frequency response, lift force, and interactive wake patterns are presented and discussed. The trends of the amplitude and frequency responses from numerical simulations are in good agreement with experimental results. The main conclusions of Reynolds number effect on interactive flow induced oscillations are: (1) Five significant flow patterns between two tandem locally-rough cylinders for different Reynolds numbers are observed through analyzing the complex but stable interactions between vortices and cylinders. (2) In the initial and upper VIV branches, the downstream cylinder's FIO is seriously interfered by the wake of the upstream cylinder. (3) The downstream cylinder is strongly impinged by the vortices shed from the upstream cylinder resulting in nearly 180O out-of-phase oscillations in transition from VIV to galloping and in-phase oscillations in galloping.

Medium- and Large-Vessel Vasculitis.

Systemic vasculitides are multisystem blood vessel disorders, which are defined by the size of the vessel predominantly affected, namely small, medium, or large vessels. The term "large vessel" relates to the aorta and its major branches; "medium vessel" refers to the main visceral arteries and veins and their initial branches. The most common causes of large-vessel vasculitis are giant cell arteritis and Takayasu arteritis, and those of medium-vessel arteritis are polyarteritis nodosa and Kawasaki disease. However, there is some overlap, and arteries of any size can potentially be involved in any of the 3 main categories of dominant vessel involvement. In addition to multisystem vasculitides, other forms of vasculitis have been defined, including single-organ vasculitis (eg, isolated aortitis). Prompt identification of vasculitides is important because they are associated with an increased risk of mortality. Left undiagnosed or mismanaged, these conditions may result in serious adverse outcomes that might otherwise have been avoided or minimized. The ethnic and regional differences in the incidence, prevalence, and clinical characteristics of patients with vasculitis should be recognized. Because the clinical presentation of vasculitis is highly variable, the cardiovascular clinician must have a high index of suspicion to establish a reliable and prompt diagnosis. This article reviews the pathophysiology, epidemiology, diagnostic strategies, and management of vasculitis.

Flow-induced vibrations of a hinged cavity at the rear of a blunt-based body subject to laminar flow

We perform numerical simulations to characterize the flow-induced vibrations (FIV) of a rear cavity with elastically hinged rigid plates, placed as a passive device at the base of a blunt body that is subject to a laminar flow of Reynolds number Re=400. The dynamic response and forcing of plates, wake features and force coefficients are investigated for the range of reduced velocity U*=[0,30]. Three different regimes of the rotational oscillations are identified. An initial branch of low oscillation amplitude is defined for U*<2.5, where the plates oscillate in counter-phase (varicose mode) with a frequency fp that corresponds to the harmonic of the wake vortex shedding frequency fp≃2fw, and is similar to the natural frequency of the plates, fp≃fn. For intermediate values of U*, the plates oscillate in phase (sinuous mode) at their natural frequency, with respect to a closer averaged location of plates. Such synchronization regime amplifies the vibration magnitude and defines the upper branch in the amplitude response curve, whose maximum is attained at U*=4.7. Due to such enhanced vibration, the vortex shedding frequency is now locked-in at the natural frequency of plates, so that fp=fn=fw. Finally, for larger values of U*, a lower branch of moderate amplitude response is defined, which is characterized by the in-phase oscillation of plates, with respect to an more open average position, governed again by the shedding frequency, fp=fw>fn. Additionally, a multibody model has been developed to retrieve, from the plates rotational motion, the resultant forces and moments that produce the plates vibration. Such inverse dynamics model is formulated to allow its generalization for configurations of higher dynamical order, and validated against the results obtained from the numerical simulations. The analysis shows that the synchronization regime is mainly promoted by a reduced fluid damping and a forcing moment that acts in phase with the plates motion. The switch in such phase from 0∘ to 180∘ occurs after the lock-in, what attenuates the plates response at large U*. In general, the FIV of plates alters the vortex shedding and near wake pressure, especially during the synchronization regime, inducing an overall increase of the global force coefficients with respect to the static cavity. Thus, the performance of hinged plates enhances generally the mean drag, although a 25% reduction is reported for the lift amplitude.

Numerical analysis of the flow-induced vibrations in the laminar wake behind a blunt body with rear flexible cavities

We present a numerical study on the fluid–structure interaction of an incompressible laminar flow around a slender blunt-based body implementing a rear cavity of flexible plates. The study focuses on the use of this type of device to control the wake dynamics and the aerodynamic forces acting on the body, as well as to harvest energy from the flow. To that aim, the effects on the plates flow-induced vibrations (FIV) and on the dynamics of the flow of three control parameters, namely the reduced velocity, 0≤U∗<12, the mass ratio, m∗=[500,1000] and the cavity height hc, are evaluated at Reynolds number Re=500. Four different branches are identified in terms of dynamic response, as U∗ increases, regardless of the values of hc and m∗. At low values of U∗, an initial branch with a local peak of moderate amplitude response is observed, where the plates oscillate in counter-phase, in a varicose mode, with a frequency fp that is synchronized with the second harmonic of the vortex shedding frequency, 2fvs, and similar to the natural frequency of the solid, fn≃f1,n. For intermediate values of U∗, a transition towards a sinuous mode of oscillation occurs, where the plate frequency is synchronized with the vortex shedding frequency, fp=fvs. Initially, after such transition, the oscillation frequency is lower than the natural frequency of the plates fp<f1,n, so that a weak response defines a lower branch in the amplitude response curve. When U∗ increases, a lock-in regime develops with fp=fvs=f1,n, that is characterized by a response amplification, giving rise to the emergence of the upper branch, where the FIV amplitude of plates is the highest. Finally, a fourth desynchronization branch of moderate amplitude appears for larger values of U∗, where the plates present a complex, multi-mode regime, characterized by the vibration at multiple frequencies within the range 5f1,n<fp<6.5f1,n. The analysis of the plates deformation through POD analysis reveals that they mainly oscillate following the first Euler–Bernoulli mode for the first three branches, and a combination of the second and first Euler–Bernoulli modes for the desynchronization branch. The effect of increasing the mass ratio is to mitigate the response at higher values of U∗, while reducing the cavity height hc leads to the fostering of oscillations within the upper and desynchronization branches. In general, the FIV response of plates alters the wake dynamics and the force coefficient, especially within the lock-in regime, where the drag is strongly amplified, although the fluctuations of the lift are attenuated (nearly a 40% reduction). Besides, reductions of the drag of approximately 2% are obtained within the initial and lower branches. Finally, a simple quantification of the energy transfer from the plates, through a linearized Euler–Bernoulli approach, shows that the lock-in regime represents the best regime to extract energy from the flow.

Modeling flow and pressure distributions in multi-branch light-commercial duct systems

This paper describes a numerical model that was developed to predict flow and pressure distribution in three multi-branch air duct systems as a function of upstream static gauge pressure. The duct systems were comprised of a combination of wire-wound flexible ducts and rigid sheet metal ducts. The model used the Darcy equation and the concept of the local loss coefficient, in conjunction with the continuity equation, to perform the calculations. The secant method was utilized to predict the flow rate through the initial upstream branch, and the Newton-Raphson method was employed model the flow through the remaining branches. The model demonstrated that the static gauge pressure rose in the overall flow direction due to the static regain effect, and that flow rate distribution varied in a predictable, characteristic manner in the overall flow direction. The model branch flow predictions were verified experimentally. The model is potentially useful for modeling the performance of variable air volume (VAV) air duct systems that use control strategies that depend on changing the fan speed and/or adjusting damper settings in the branches.

Identification of upper branch for vortex-induced vibration of a circular cylinder at [formula omitted

In this study flow around a circular cylinder undergoing transverse-only vortex-induced vibrations is investigated using a two-dimensional in-house CFD code. The Navier–Stokes equations, the continuity and pressure Poisson equations written for an incompressible constant property Newtonian fluid coupled with the structural equation are solved using the finite difference method. Systematic computations are carried out for different damping ratio values between ζ=0% and 5%. Reduced velocity is varied in U∗=2.5−7.5, while Reynolds number and mass ratio are fixed at Re=300 and m∗=10, respectively. Up until now, researchers have reported an upper branch only at high Reynolds numbers and low m∗ζ values. However, in this study we have observed a three-branch behavior (initial, upper and lower branches) at Re=300 for ζ≤1%. The upper branch is bounded by two gradual phase changes: at the boundary adjacent to the initial branch, the time-averaged phase difference of vortex force, and at the boundary to the lower branch, the time-averaged phase difference of transverse fluid force relative to the cylinder displacement changes between 0° and 180°. Unbounded variations and phase slips are observed in the time-dependent phase differences, which explains the gradual changes in their time-mean values. In some ranges of the upper branch the second harmonic frequency component plays an important role in the spectra of transverse fluid force, which is closely related to the observed asymmetrical vortex structure. Increasing the structural damping above ζ=1%, only initial and lower branches are found. The comparison of peak oscillation amplitude against an empirical relationship provided in the literature shows very good agreement for ζ≥1%. A Griffin plot is also used for the comparison of peak response data where the currently obtained results and those in the literature collapse onto almost a single curve.

Establishment of Decision Rules and Risk Assessment Model for Preoperative Prediction of Lymph Node Metastasis in Gastric Cancer.

Background: Preoperative accurate prediction of lymph node status is especially important for the formulation of treatment plans for patients with gastric cancer (GC). The purpose of this study was to establish decision rules and a risk assessment model for lymph node metastasis (LNM) in GC using preoperative indicators.Methods: The clinical data of 554 patients who underwent gastrectomy with D2 lymphadenectomy were collected. A 1:1 propensity score matching (PSM) system was used, and the clinical data of the matched 466 patients were further analyzed. The important risk factors for LNM were extracted by the random forest algorithm, and decision rules and nomogram models for LNM were constructed with a classification tree and the “rms” package of R software, respectively.Results: Tumor size (OR: 2.058; P = 0.000), computed tomography (CT) findings (OR: 1.969; P = 0.001), grade (OR: 0.479; P = 0.000), hemoglobin (Hb) (OR: 1.211; P = 0.005), CEA (OR: 1.111; P = 0.017), and CA19-9 (OR: 1.040; P = 0.033) were independent risk factors for LNM in GC. Tumor size did rank first in the ranking of important factors for LNM in GC and was the first-level segmentation of the two initial branches of the classification tree. The accuracy, sensitivity, specificity, and positive predictive value of the decision rules in diagnosing preoperative LNM in GC were 75.6, 85.7, 73.9, 73.5, and 79.3%, respectively. The accuracy, sensitivity, and specificity of the risk assessment model in predicting preoperative LNM in GC were 79.3, 80.3, and 79.4%, respectively.Conclusion: Tumor size was the most important factor for evaluating LNM in GC. This decision rules and nomogram model constructed to take into account tumor size, CT findings, grade, hemoglobin, CEA, and CA19-9 effectively predicted the incidence of LNM in preoperative GC.

EVALUATING THE EFFECT OF APERTURE VARIATION ON THE HYDRAULIC PROPERTIES OF THE THREE-DIMENSIONAL FRACTAL-LIKE TREE NETWORK MODEL

Hydraulic properties of rock fractures are important issues for many geoengineering practices. Previous studies have revealed that natural rock fractures have variable apertures that could significantly influence the permeability of single rock fractures, yet the effect of aperture variation on the hydraulic properties of fractured rock masses has received little attention. The present study implemented a series of flow calculations on two kinds of 3D fractal-like tree network models constituted by fractures with heterogeneous aperture distributions and parallel plates with uniform apertures to gain insight into the effect of aperture variation on the hydraulic properties of fractured rock masses. The fluid flows through the two kinds of models are simulated using a developed numerical code, whose validity is verified by comparisons with the analytical solutions and previous experimental results. The effects of heterogeneous aperture distributions on the permeability of the models are illustrated by changing the geometrical parameters including the aperture ratio and mean aperture of the initial fracture branch. The results show that a significant channeling flow is observed in the 3D fractal-like tree network models constituted by fractures with heterogeneous aperture distributions. These preferential flow paths are mainly located in the large aperture channels, bypassing the contacts and/or low aperture barriers. The equivalent permeability of the 3D fractal-like tree network models increases with increasing fracture aperture ratio and/or increasing mean aperture of the initial fracture branch. The permeability ratio of the model of fractures with heterogeneous aperture distributions to the model with uniform mean apertures is always smaller than 1.0, and the ratio increases following a logarithmic relationship as the mean aperture of the initial fracture branch increases. A regression function is proposed to estimate the equivalent permeability of the model of fractures with heterogeneous aperture distributions. The deviations between the predicted permeability and the simulated/experimental results are less than half of the order of magnitude, which verifies that the proposed equation is capable of predicting the equivalent permeability of 3D fractal-like tree networks as a first-order estimation.

Flow control and vibration response of a circular cylinder attached with a wavy plate

Flow past a circular cylinder fitted with a rear rigid wavy plate at a low Reynolds number of Re = 150 is first numerically studied in this work. The effects of the plate length and the surface undulation on the hydrodynamic forces and vortex shedding behavior of the circular cylinder are examined. The mean drag coefficient and the fluctuation of lift coefficient are reduced up to 27.5% and 54.9%, respectively, in the presence of a wavy plate. Additionally, the vortex formation length is elongated and the wake width is shortened, illustrating the suppression of vortex shedding. According to the flow control performance, the 1.5D-length (D is the cylinder diameter) wavy plate with wavelength of 3D is employed to control the vortex-induced vibration (VIV). The two-degree-of-freedom of flow-induced vibration is computed for a wide range of reduced velocities (Ur = 2–20) in comparison with a bare cylinder. The results indicate the initial and lower branches of VIV are effectively suppressed by the wavy plate with the maximum reduction of cross-flow amplitude up to 92.44%. Nevertheless, the reattachment of shear layers on the wavy plate surface and the asymmetric P + S (a single vortex and a pair of opposite signed vortices released per cycle of shedding) vortex structure stir the galloping instability at Ur > 8, instead of the desynchronization branch. The monotonic increase of vibration amplitude in galloping branch shows a greater potential for energy harvesting.

The Long-term Fate of Aortic Branches in Patients With Aortic Dissection

ABSTRACT Objective Late morbidity and mortality related to aortic branches in patients with aortic dissection (AD) are not well described. We aimed to investigate the fate of aortic branches in a population cohort of patients with newly diagnosed AD. Methods We used the Rochester Epidemiology Project record linkage system to identify all Olmsted County, MN, residents diagnosed with AD from 1995 to 2015. Only patients with >30 days of available follow-up imaging were included in the analysis. The primary outcome was freedom from any branch-related event (any intervention, aneurysm, malperfusion, rupture, or death occurring after the acute phase >14 days). Secondary outcome was the diameter change of the aortic branches. Univariate and multivariable Cox proportional hazards models were used to identify predictors of branch-related events; univariate and multivariate linear regression models were used to assess aortic branches growth rate. Results Of 77 total incident AD cases, 58 patients who survived with imaging follow-up were included, 28 (48%) with type A and 30 (52%) with type B AD. The presentation was acute in 39 (67%) cases; 6 (10%) had branch malperfusion. Of 177 aortic branches involved by the AD, 81 (46%) arose from the true lumen, 33 (19%) from the false lumen, 63 (36%) from both. After the acute phase, freedom from any branch-related event at 15 years was 48% (95%CI 32-70). Thirty-one branch-related events occurred in 19 patients over 15 years: 12 interventions (76% freedom, 95%CI 63-92), 10 aneurysms (67% freedom, 95%CI 50-90), 8 malperfusions (76% freedom, 95%CI 61-94) and 1 rupture (94% freedom, 95%CI 84-100). There were no branch-related deaths. Type B AD (HR 3.5, 95%CI 1.1-10.8; P=.033), patency of the aortic false lumen (HR 6.8, 95% CI 1.1-42.2; P=.038) and malperfusion syndrome at presentation (HR 6.0, 95% CI 1.3-28.6; P=.023) were predictors of late aortic branches-related events. Overall growth rate of aortic branches was 1.3±3.0 mm/year. Patency of the aortic false lumen, initial branch diameter, and Marfan syndrome were significantly associated with diameter increase. Conclusions In patients with AD, aortic branch involvement was responsible for a significant long-term morbidity, without any related mortality. Type B AD, patency of the aortic false lumen, or malperfusion syndrome at presentation had a higher risk of branch events during the long-term follow-up. Dilatation of the aortic branches was observed in one third of cases during follow-up, in particular in case of a patent aortic false lumen or Marfan syndrome.

Biomass and Coppicing Ability of Genetically Improved Calliandra calothyrsus for Wood-Energy with Different Spacing

Beside wood quality, biomass and ability to coppice of fast-growing woody species for renewable energy are two essential indicators. Appropriate spacing among individual plant is therefore required to get the best harvest. This study is observing biomass, branching and coppicing ability of Calliandra calothyrsus at different spacings. Initial experimental plots were using 5 blocks of 16 individuals at spacings of 0.5x1; 1x1; 0.5x2; 1x2 and 2x2m and assessed at 6 months old around reproductive stage. Due to no significant differences, two spacing plots of 2x1 and 1x1m are compared for biomass and wood dimension assessment from 14 individuals per block replicated into 4 blocks after 3 years. Coppicing ability was counted after 2 months of felling. The results indicated that diameter has positive correlation with number of initial branches as well as number of coppices. Specific gravity of wood is also increasing with diameter. Between the two types of spacing, the first wood production is better for 1x1m than 1x2m with 76.3 ton/ha (152 m3/ha) for 1x1m and 72 ton/ha (144 m3/ha) for 1x2m. This indicates a better production than the predicted MAI from the breeding. Specific gravity is recorded to be better at more spaciuos distance.

Transverse displacement phase analysis on 2DOF FIV of rigid cylinders in tandem configurations

With the development of offshore oil production and the resulting application of riser pipes, it is necessary to get a better understanding of the flow-induced vibrations (FIV) phenomenon involving multiple cylindrical structures. In this scenario, little is available concerning the phase difference between the transverse displacements of two long rigid cylinders (aspect ratio of 30) in tandem and free to vibrate due to the flow incidence. Aiming to fill this gap, experiments were carried out at the towing tank of the Technological Research Institute (IPT) for two similar rigid cylinders in a tandem arrangement. Both cylinders were elastically supported with two degrees of freedom (2DOF), the in-line and transverse direction. Different tandem distances were tested ( $$T=2D$$ , 2.5D, 3D, 4D and 6D) throughout the complete excitation of the lock-in range for the upstream cylinder, i.e., reduced velocities ranged from 3 to 13, which corresponds to Reynolds numbers from $$3\times 10^3$$ to $$3\times 10^4$$ . This work found the upstream cylinder having a qualitatively similar response compared with the isolated one. The downstream cylinder exhibited large response amplitudes compared with the upstream one in the lower branch of vibration. Lastly, the phase difference between transverse displacements of both cylinders was classified according to five phase patterns, two of them apparently related to the initial and upper branches of vibration in all cases.

On the formation of Taylor-Görtler structures in the vortex induced vibration phenomenon

In this work, the three-dimensional structure of the boundary layer in the context of the vortex induced vibration of a circular cylinder is presented and investigated for the first time. Large-eddy simulations of a low mass ratio (m=2.6) two-degrees of freedom circular cylinder at the subcritical Reynolds number Re=5300 and zero damping (ζ=0) for several reduced velocities of the system have been performed. A detailed description of the flow topology at the cylinder boundary layer and in the near wake for the three branches of structural response, i.e. the initial (I), super-upper (SU) and lower (L) branches, is presented. In the SU branch, the boundary layer becomes three-dimensional due to the emergence of streamwise vortices which are associated to the onset of a centrifugal instability that occurs twice every cycle. This is the first time a centrifugal instability in a freely vibrating system is reported. The streamwise structures with alternating vorticity, called here Taylor-Görtler vortices, are described and characterised. It is shown that their wavelength is in agreement with that of other centrifugal instabilities observed in forced sinusoidal oscillating cylinders.

Vortex-induced vibrations of a confined circular cylinder for efficient flow power extraction

The effects of confinement on vortex-induced vibration (VIV) of a circular cylinder (diameter D) and its flow power extraction capability are presented. A two-dimensional numerical study is performed on VIV of a circular cylinder inside a parallel plate channel of height H at Reynolds numbers 100 and 150. The blockage ratio (b = D/H) is varied from 1/4 to 1/2. The cylinder is elastically mounted with a spring such that it can only vibrate transversely to the flow. It has a fixed non-dimensional mass (m*) of 10. The energy extraction process is modeled as a damper (damping ratio ζ) attached to the cylinder. With increasing blockage, the vibration amplitude of the cylinder decreases, the lock-in happens at a larger non-dimensional natural frequency of the cylinder, and the initial branch of the vibration response of the cylinder shrinks. There is a minimum value of the channel height and Reynolds number for the existence of the initial branch. The extracted power is found to increase rapidly with the blockage. For the maximum blockage (b = 1/2), the flow power extracted by the cylinder is an order of magnitude larger as compared to what it would extract in an open domain with free stream velocity equal to the channel mean velocity. The optimal mass-damping (α = m*ζ) for extracting the maximum power is found to lie between 0.2 and 0.3. An expression is derived to predict the maximum extracted power from the undamped response of a confined/unconfined cylinder.

In silico identification of three putative SWEET genes in Metroxylon sagu

Recent studies have identified Sugars Will Eventually be Exported Transporters (SWEET), a novel type of sugar transporters in diverse plant species. This gene family selectively transports different kinds of sugar substrates, including sucrose, fructose and glucose. In this paper, three Metroxylon sagu SWEET genes (MsSWEET-X, MsSWEET-Y and MsSWEET-Z), predicted to be involved in starch accumulation, were identified from the NCBI EST database. A comparative analysis was carried out against Arabidopsis thaliana TAIR and Elaeis guineensis NCBI genome databases resulting in amino acid residues similarity of three MsSWEET genes of 21.32 to 76.25 %. One full-length coding sequence (CDS) of 229 amino acids from MsSWEET-X has been annotated as opposed to the partial CDSs from the other two. Three types of putative protein domains (Calreticulin, Glycosyl hydrolases and Triose-phosphate transporter) were predicted for MsSWEET-X, MsSWEET-Y and MsSWEET-Z, respectively. Multiple Alignment sing Fast Fourier Transform (MAFFT) has identified three conserved amino acid motifs (Motif-A, Motif-B and Motif-C) among three compared species. Phylogenetic analysis using Maximum-Likelihood Estimation has revealed two genes AtCRT3 and MsSWEET-X at the upstream of initial tree branches (0.17 and 0.12 length) showing their early evolutionary orthology. By contrast, MsSWEET-Y gene was predicted to be the latest homolog of SWEET16 and SWEET17 undergoing speciation events from both Arabidopsis and oil palm. Taken together, these results showed that even though the oil palm and sago palm shared the common ancestry of monocotyledonous family, their SWEET genes were divergent. The gene MsSWEET-X was highly close to its homolog in Arabidopsis.

The effect of axis ratio on the vortex-induced vibration of an elliptical cylinder

A numerical investigation is conducted to study the vortex-induced vibration (VIV) of an elliptical body subjected to transverse oscillation with the non-dimensionless mass (mr ) fixed to be 10 and Reynolds number set to be 100. Three sets of axis ratio (Λ) are considered in the analysis where, Λ is defined as the ratio of the major and minor axis, with minor axis aligned parallel to the flow. Spectral/hp element-based software, Nektar++ is employed for the solution of incompressible flow equations. The computations are conducted for reduced velocity ranging from 2≤U* ≤9. The amplitude response is directly proportional to the increase in axis ratio in association with the pre-initiation of lock-in regime for higher axis ratio. It is also noticed that the initial branch gets widened, whereas the lower branch is constricted when the axis ratio of the cylinder is increased. However, the vortex shedding pattern in all the branches is observed to be 2S and its various modes.